Identifying Synapomorphies in the Flowers ofHoyaandDischidia—Toward Phylogenetic Understanding

HoyaandDischidiaare closely related genera, but molecular phylogenetic analyses have not succeeded in revealing their exact relationship. The morphology of the pollinating apparatus, consisting of guide rails, stamens, pollinaria, and stigmas, of selected species ofHoyaand ofDischidia, as well as ofStephanotis floribundaand ofMarsdenia cordifolia, is examined and discussed in the light of the mechanisms involved in the pollination of their flowers. Flowers ofHoyahave generally lost their inner guide rails, while guide rails inDischidiaare more developed and often provided with inner rails. Nectar inHoyais produced from a tube in the guide rails but also by secondary nectaries positioned inside the anther skirt. The pollinium in this genus is, in the majority of cases, provided with a pellucid margin that is inserted into the guide rails during pollination. Pollinia ofDischidiahave crested caudicles, which because of structural similarity to the pellucid margins ofHoya, are hypothesized to fulfill the same function. Pollinia with pellucid margins together with modified guide rails and secondary nectaries inside the anther skirt support the monophyly ofHoyaand point to a systematic position ofDischidiaoutside this genus in the tribe Marsdenieae.